There are known a number of heat-sensitive recording materials of the type that is so designed as to produce a record image when a color former and a color developer are brought into contact with each other by heat. Those heat-sensitive recording materials of this type are comparatively inexpensive and suitable for use on a compact recording machine, which is relatively easy in its maintenance. In fact, they are used as a recording medium in facsimile system, various computer systems, medical instruments, heat-sensitive copying systems, and printers of other various instruments.
In recent years, various information instruments have been developed and they have been used in various sectors. Along with this situation, various demands have been made for the heat-sensitive recording material to be used as a recording medium in those information instruments.
For instance, as for the facsimile system, there have been commercialized various minimized facsimile systems of improved high recording speed. In this respect, there is an increased demand for providing an improved heat-sensitive recording material which capable of instantly and precisely responding to a slight printing energy to record high quality clear images excelling in gradation and resolution corresponding to information signals transmitted. Other than this, in recent years, various video-printers capable of providing high quality photograph-like images have been commercialized. For the heat-sensitive recording material to be used for recording information outputted from those printers, it is demanded to be such that can provide a sufficient recording density (optical density) in the entire density range from low density region to high density region, satisfactory gradation and resolution (reproduction of dots) for images obtained. Further, various bar code printers of handy type have been commercialized in recent years. For the heat-sensitive recording material to be used in those printers, there is also the same increased demand as in the case of the foregoing facsimile system.
To meet the above demands, there have been made developed relevant color formers, color developers and sensitizers. There have been made proposals also on the substrate on which a heat-sensitive recording layer is to be disposed. That is, as the substrate, use of a synthetic sheet such as foamed polyolefin film or an opaque synthetic resin film such as polyolefin resin film containing a pigment has been proposed aiming at improving the resolution of an image to be provided. However, for the heat-sensitive recording material having the substrate comprising a foamed polyolefin film, although it is satisfactory in its recording sensitivity and there can be obtained images satisfactory in resolution, there is a problem that the substrate is not sufficient in its heat resistance and because of this, the portions of the heat-sensitive recording material on which images are to be recorded are likely to deform due to heat at the time of recording by a thermal head and to cause local extension or curling on the heat-sensitive recording material.
Especially, when the foregoing heat-sensitive recording material is used in the foregoing videoprinter or bar code printer, since images having solid parts (whole black parts) in greater numbers in comparison with the images of character informations are recorded thereon, the above problems are often caused to make the resultant recorded product accompanied with deformed portions due to local extensions and/or curlings.
In this consequence, there is an increased demand for providing a desirable heat-sensitive recording material which is free of the foregoing problems found on the known heat-sensitive recording material and which provides a desirable image-recorded product in any of the recording systems.